The objectives of this K08 proposal are two-fold: 1) to provide the candidate with the essential scientific and professional skills to become an independent physician-scientist focused on the molecular and cellular pathogenesis of pulmonary hypertension, and 2) to investigate the mechanisms underlying pathologic pulmonary arterial smooth muscle cell (PASMC) proliferation and migration in pulmonary arterial hypertension (PAH). Dr. Huetsch and his mentor, Dr. Larissa Shimoda, have designed a training plan that combines laboratory experience, coursework, and professional mentorship to foster expertise in experimental design and techniques, data analysis, and scientific communication. This training will occur through the investigation of a novel signaling pathway underlying PASMC dysfunction and pulmonary vascular remodeling in PAH, a disease which continues to cause significant morbidity and mortality owing to the lack of therapies designed to reverse vascular remodeling. Based on our preliminary data, we hypothesize that, in PAH, increased calpain activity in PASMCs leads to activation of Ca2+/calmodulin dependent protein kinase II (CaMKII), which then induces increased activity of the Na+/H+ exchanger (NHE), resulting in pathologically elevated PASMC proliferation and migration and pulmonary vascular remodeling. Using PASMCs isolated from PAH patients as well as the Sugen/hypoxia rodent model of PAH, we plan to investigate this hypothesis through three aims: 1) to determine whether calpains are necessary for vascular remodeling in PAH, 2) to determine whether CaMKII is necessary for vascular remodeling in PAH, and 3) to determine whether NHE is necessary for vascular remodeling in PAH. We plan to utilize genetic, molecular, and pharmacologic techniques to induce gain-of- function and loss-of-function of each component of this pathway with subsequent measurements of 1) activity of downstream components of the pathway, 2) PASMC proliferation and migration in vitro, and 3) prevention and/or reversal of pulmonary vascular remodeling in vivo. Accomplishment of these aims will provide a rigorous training program for Dr. Huetsch and uncover novel mechanisms underlying pathologic PASMC function in PAH which could hopefully be translated into new therapeutic targets.